The applicants have produced a bending machine, known as the "Langbow Multiplane Tube Bending Machine Model TM32-5AX", which comprises two base units, each of which carries a bending unit, and, between the base units, an apparatus for holding and turning a tubular workpiece about a predetermined axis passing through the bending units.
Said apparatus comprises a clamping jaw member disposed between two abutment jaws members, which jaw members are co-axial with said predetermined axis. The periphery of each jaw member is near circular, is interrupted to provide a mouth and is provided with outwardly projecting gear teeth to serve as an interrupted ring gear. Within each jaw member the mouth leads to a part-circular socket, co-axial with said axis to receive a tubular workpiece of predetermined diameter. In the clamping jaw member there is a protruding wedge which extends inwards into a part of the socket adjacent to the mouth. The jaw members are mounted in a body and are engaged by respective toothed hydraulically driven racks actuable to move the jaw members through a restricted arc of a circle about said axis. The rack engaging the clamping jaw member can be moved, firstly, independently of the other racks to move the mouth of the clamping jaw member between an open position (in which the mouths are aligned) and a clamping position displaced from the open position so as thus to ram the wedge against the workpiece; and, secondly, in unison with the abutment jaw members.
This apparatus is intended to hold and turn the workpiece about said axis to permit the planes between the bends made by the bending units to be varied angularly, but several problems have arisen, from limitations inherent in this apparatus, including damage to the workpieces, imprecise angular adjustment or location of the workpieces and difficulties in loading the workpiece into the sockets in respect of some forms of tubing. Further problems have arisen because the apparatus cannot accommodate certain requirements for bending workpieces rapidly, for accepting workpieces of different diameters without changing the jaw members, for turning the workpieces through some ranges of angles and for accurate initial orientation of the workpieces.
The apparatus has, however, many advantages which make it particularly effective for use in mass-producing relatively complex shapes from constant-single-diameter workpieces provided that the angles between the planes of adjacent bends lie within certain limited ranges and need to be only approximately accurate to within a few degrees, e.g. for producing wheelbarrow chassis.
An object of the present invention is to enable said problems to be overcome or reduced, and to improve said advantages.